Qubits are 2-level systems suitable for control over the level
occupation including superpositions. In solid state, two qubit
examples are the effective 2-level system in appropriately
designed superconducting devices and single-electron spin
states in semiconductor quantum dots. Qubit control is
demonstrated with NMR-type pulse techniques such as Rabi flops
and spin-echo. The readout of a qubit state is an important
part of the qubit circuit since any backaction can shorten the
coherence lifetime. We discuss a recent realization of a
single-shot readout of the spin of a single electron.